Heater control system with combination modular and daisy chained connectivity and optimum allocation of functions between base unit and local controller modules

ABSTRACT

A heater control system that utilizes electronic temperature control at each of a number of interconnected heaters is provided for monitoring and operating heaters within a narrow temperature range. In one embodiment, a heater control system is provided that is adapted for controlling a number of heaters positioned on pipe and components of a piping system from a remote location. The heater control system includes satellite controllers mounted on each heater connected daisy chain fashion and includes a monitoring station with a user interface for allowing a user to monitor and to remotely control the operating status or temperature of each heater in the heater control system. To satisfy the user&#39;s space requirements, the size of each controller is maintained at a small form factor and a single cord is used to provide power and communications lines to and between the controllers. Each controller integrates power supply and control with electronic temperature control to minimize the use of mechanical switching and to increase the accuracy of temperature control. The temperature set point is adjustable at each controller and, in one embodiment, the temperature set point is remotely adjustable from a remote monitoring station. The operating status of each controller is displayed on the exterior of the controller&#39;s housing and in one embodiment, the operating status, such as temperature, is displayed at a base station for each line of controllers and heaters and on a user interface monitor at a monitoring station.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is a continuation-in-part of U.S. patentapplication, Ser. No. 09/553,416, filed Apr. 20, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a system forcontrolling and monitoring the temperature of heaters, and moreparticularly, to a heater control system for a plurality of individualpipe heaters positioned adjacent each other on a pipe with a like numberof controller modules, which are configured for daisy chain connectiontogether and for individual connection to individual mounting on andpipe heaters to provide individual electronic temperature and powercontrol at each of the pipe heaters.

[0004] 2. Description of the Related Art

[0005] The use of pipe heaters is widespread in semiconductormanufacturing, chemical, and pharmaceutical processing, plasticsmanufacturing, food processing, and other industries to heat pipingsystems to control various production and waste processes. Typically,the temperature of the piping system must be kept within a certaintemperature range to keep gases or liquids flowing in the pipes atdesired temperature levels as they are transported from one place toanother. For example, in the semiconductor manufacturing industry,flexible insulated heaters, such as those disclosed in U.S. Pat. No.5,714,738 to Hauschulz et al., are installed along the length of pipingand piping components downstream from a reaction or deposition chamberto maintain transported effluent gases and vapors within specifictemperature ranges that prevent the effluent gases and vapors fromreacting, condensing, or depositing and building up solids on insidepipe walls, in valves, and in other pipe components before they can betrapped and removed in a cost effective manner.

[0006] In many industrial applications, the acceptable temperature rangefor the piping is tight or small, i.e., within a few degrees of a setpoint, and sometimes, the set point temperature is relatively high,e.g., above 180° C. Also, some pipes are fairly long and heat transferrates may vary in different locations, so individual control of numerousindividual pipe heaters positioned along the length of a pipe is neededto prevent development of local hot spots or cold spots. Therefore,there is a significant demand for an accurate and responsive heatercontrol system that allows the user to obtain and maintain temperaturesof piping components within user selectable ranges, including capabilityof controlling individual pipe heaters to deliver different heatingpower to various pipe locations as needed to maintain a desiredtemperature profile. Further, because consequences of individual heaterfailures can be quite expensive due to down time for the manufacturingprocess to disassemble and clean or replace clogged or damaged pipes,valves, and other components, heater control systems should be able toprovide the user with operating information during use, such as whetherthe heater is “on” or “off” and whether the heater is within a specifiedtemperature range. Pipe heaters often have to be installed on pipingcomponents that are small, such as 2-inch or smaller diameter piping,and in places where there is little or no clearance between pipingcomponents and adjacent structures. Therefore, users of the heatersoften need heaters and associated control equipment that is not bulky ordifficult to install, that is durable enough for industrial use, andthat is easy to maintain and/or replace. Of course, the heaters andheater control systems must be configured to meet any and all safetystandards (e.g., electrical and fire safety standards) that may apply tothe particular industry.

[0007] One approach that is currently used to provide pipe heatercontrol is to use an individual, self-contained, electromechanicaltemperature controller installed on each heater. With respect topipeline heaters, these electromechanical temperature controllers aretypically either bimetallic snap-action or creep-action thermostats,which are generally compact in size and relatively inexpensive.Unfortunately, such temperature controllers that utilize bimetallic orother snap-action or creep-action type thermostats generally have asingle, fixed temperature set point and provide only limited temperaturecontrol.

[0008] In this regard, most snap-action electromechanical temperaturecontrollers have a 15° C. or larger hysteresis or deadband around a setpoint temperature, which is unacceptable for applications that requiretight pipe temperature control within only a few degrees of set point.Creep-action thermostats offer tighter initial temperature control, butthey then become inaccurate as they drift over time. They also haveshort service lives due to high levels of electric arcing that occursbetween their switch contacts. Also both of these types ofelectromechanical temperature controllers must be configured andinstalled such that there is intimate thermal contact with the activeheater surface of the pipeline heater to function properly. Therefore,the general practice is to permanently embed the electromechanicaltemperature controller within the pipeline heater, and when thethermostat fails or needs servicing, the entire heater with controllermust be replaced and typically scrapped. Another problem with mostelectromechanical temperature controllers is that they provide little orno operating information during use, and to find a non-functioningheater, operating or maintenance personnel have to touch each of theheaters with their hands to determine if it is warm and therefore,presumably operating. Additionally, the users of these heaters often areleft without any accurate information on the actual operatingtemperature of the heater.

[0009] Another approach to heater control for pipes is the use ofelectronic temperature controllers that are positioned remote from theheaters and communicate via numerous individual data and power lineswith extending from the remode controller to each heater. While suchelectronic temperature controllers, when combined with thermocouples,provide improved control of each heater and a tighter temperature range,they are relatively costly, and the large bundles of wires arecumbersome to install, especially in tight spaces. The high cost percontroller and tangle of wires has led many users to bundle severalheaters together in a zone or piping portion and to place the entirezone under the control of a single controller. While that solutiondecreases the complexity and tangle of wires, it also results in all thepipe heaters in a zone being set to a single temperature and, of course,the accuracy of control decreases with the overall size of the zone. Forexample, such a zone typically comprises one master and one or moreslave heaters. The temperature sensor used by the single electroniccontroller is located near or connected to the master heater, and thetemperature sensed at this single point in the piping system drives theheater control for all the heaters in the zone. However, the thermalloading, i.e., heating power needed, a temperature profile may be, andoften is, different at each of the individual slave heater locations.Also, there is no way to ensure that individual slave heaters in a zonedo not run arbitrarily hotter or colder than the master heater, whichleads to decreased accuracy or tightness in controlling the temperaturethroughout the piping system or zone.

[0010] The use of a single controller to operate an entire zone may alsocreate safety issues. For example, if the master heater fails cold orlow, the controller typically operates or controls the other properlyoperating heaters in the zone to run hotter and overheat the rest of thepiping system. In other words, the slave heaters are not properlycontrolled within the zone, and thermal “run away” result in blown fusesand/or fires, which cause safety hazards and significant down timewithin the manufacturing facility.

[0011] Additionally, the central controllers for systems in which acentral controller is wired to control many individual heaters arerelatively large, e.g., 48 mm by 96 mm by 100 mm and must be locatedremote from the heaters due to space and mounting constraints within thetypical industrial setting. The size of each central controller becomesmore of a problem in practice because a protective cage is often placedaround the controller to protect sensitive electronic components frominadvertent damage from high temperature sources and physical contact.Further, installation and maintenance of the remotely-located centralcontrollers for a large number of individual heaters are problematicbecause of the number of wires that must be run between the centralcontroller and each heater. These wires generally include a power supplyline for providing AC power to each heater from the controllers and atemperature sensor line to connect the controller to the thermocouple orother temperature sensing device. For safety and convenience, thesewires are often strapped or bundled together, which makes it harder formaintenance personnel to work on a single heater, yet unbundling leavesan even more undesirable tangle of wires. Such “rat's nest” of wiring inthe piping system that makes maintenance, upgrading, and troubleshootingof these heater control systems time consuming and difficult foroperating and maintenance personnel.

[0012] Consequently, there remains a need for an improved heater controlsystem for providing enhanced control and monitoring of individualheaters in pipe heating systems, but without the concomitant wiring andcontroller complexity and physical size that is typically associatedwith such systems.

SUMMARY OF THE INVENTION

[0013] A general object of this invention is to improve individualheater temperature control equipment for pipe heating systems thatcomprise a plurality of pipe heaters, while minimizing physical size,wiring complexity, and installation, maintenance, and removalinefficiencies.

[0014] Another object of this invention is to provide a pipe heatercontrol system that combines the advantages of individual temperatureset point adjustment and temperature control in a modular, easilyinstallable and removable structure at each heater with central power,monitoring, and control functionality.

[0015] Another related object of the present invention to provide aheater control system which provides a user with improved heatermonitoring and troubleshooting capabilities.

[0016] A further object of the present invention to provide a heatercontrol system that is simple, cost-effective, and safe to install andmaintain in typical industrial environments that generally imposesignificant space restraints on the installation of additionalequipment.

[0017] Additional objects, advantages, and novel features of theinvention will be set forth in part in the description that follows, andin part will become apparent to those skilled in the art uponexamination of the following or may be learned by the practice of theinvention. The objects and the advantages may be realized and attainedby means of the instrumentalities and in combinations particularlypointed out in the appended claims.

[0018] To achieve the foregoing and other objects and in accordance withthe purposes of the present invention, as embodied and broadly describedtherein, a pipe heater control system is provided that generallyoptimizes temperature setting, controlling, and monitoringfunctionalities along with power sourcing and distribution amongindividual satellite heater controllers at each pipe heater and a basecontroller station remote from the individual heaters in order tominimize individual satellite heater controller size and wiringcomplexity. Individual temperature set point and temperature controllerfunctionality is allocated to individual local controller modulesmounted on individual pipe heaters, where they are most effective,convenient, and efficient, while power sourcing and individual heatertemperature monitoring functions are allocated to a remote base unitpositioned someplace away from th pipe heaters, where heat generated bypower source circuits can be dissipated more readily and where bulkytemperature monitoring circuits and hardware can be accommodated moreeasily. Further, the individual local controller modules are configuredfor simple “plug in” installation and “pull out” removal at theindividual pipe heaters in a manner that is exceptionally convenient,yet preserves temperature sensing accuracy while accommodating daisychain connection of a plurality of heaters and satellite controllermodules to the remote base unit. Each heater has a temperature sensorembedded by a heat insulation coating adjacent the heat producingcomponent of the pipe heater and a socket on the exterior surface of thepipe heater comprising a circuit board with two plug-type electricalconnectors for daisy chain connection of power and data cords, plug-typeelectrical connectors for connecting a local controller module to theheater, and contacts and embedded traces for: (i) routing AChigh-voltage power from one daisy chain connector to the other, to thelocal controller module, and to the heat producing component; (ii)routing dc low-voltage power from one daisy chain connector to the otherand to the local controller module; (iii) routing temperature sensorsignals from the temperature sensor to the local controller module; and(iv) routing data communication links from one daisy chain connector tothe other and to the local controller module. An individual pipe heatercan be connected to the base unit by simply plugging a daisy chain cordfrom another pipe heater into the socket, and a local controller modulecan be connected to the pipe heater and to the base unit by simplyplugging the local controller module into the socket. If a particularpipe heater is the first in a daisy chain line of pipe heaters, it andits local controller module can be connected to the base unit by simplyplugging an extension cord from the base unit into the receptacle. Eachdaisy chain cord and the extension cord has wire conductors for: (i) AChigh-voltage power; (ii) dc low-voltage power; and (iii) datacommunications links.

[0019] As an alternative, each local controller module can be equippedwith its own individual dc low-voltage power supply powered by thehigh-voltage AC power, which would eliminate the need for wireconductors in the daisy chain cord and in the extension cord. However,currently available circuits that convert high-voltage AC to low-voltagedc power for use in electronic circuits produce significant amounts ofheat that has to be dissipated to prevent damage to electric circuitcomponents. Dissipation of such heat next to a pipe heater that is alsoproducing large quantities of heat is not efficient and requires bulkyheat sink material with fins or some other heat dissipation device.Therefore, while it may be desirable to provide a dc low-voltage powersupply as a part of each local controller module, having to also addheat dissipation equipment would make th local controller module larger,heavier, and more unwieldy. On balance, with current dc power supplycircuits, it is deemed preferable to add the low voltage dc powerconductors to the daisy chain cord and extension cord and to place thedc power supply in the base unit.

[0020] As another alternative, a central processing station can beconnected to one or more base units to monitor the pipe heaters in oneor more daisy chains at a supervisory central location and to sendcontrol signals through the base stations to individual local controllermodules.

[0021] According to one aspect of the local invention, the controllermodules are designed to integrate accurate electronic temperaturesensing with power delivery control. In this regard, a preferredembodiment of the invention includes electronic components and circuitryto provide either on/off control or proportional-integrated-derivative(PID) temperature control to effectively control by electronic switchingthe operation of a heat-producing element or component of the pipeheater. The components generally include a temperature sensor, such as athermistor, positioned adjacent the heat-producing element or componentfor sensing temperature and a zero voltage switch with a triac forcontrolling heater operations quickly without arcing based on the sensedtemperature. This electronic temperature sensing and control allows thetemperature to be maintained within 4 to 5° C. or even more tightlyabout a temperature set point.

[0022] According to another aspect of the invention, the localcontroller modules are adapted for individual set point temperatureadjustment either manually at each local controller module or remotelyvia data connection from a supervisory central monitor via the basestation and data communication links. This feature allowsuser-selectable, and, if desires, differing temperature settings alongthe length of a piping system, which may be useful for numerous processapplications and overcomes the problem with prior art devices which useda single, remotely-located controller for numerous heaters connectedtogether in a zone (i.e., that provided the same temperature set pointfor all heaters connected to the remotely-located controller).

[0023] Preferably, each of the local controller modules include visualdisplay devices, such as color LED's, for indicating the operatingstatus of the pipe heater on which it is mounted. In one embodiment,three LEDs are used to show an “in-temperature-range” status, an“under-temperature-range” status, and an “over-temperature-range”status. Alternatively, or in addition, monitoring of the localcontroller modules and pipe heaters can be accomplished remotely byincluding an LED or other display at the base station to indicate, forexample, when a daisy chain line has a pipe heater that is undertemperature range, when all the pipe heaters in a daisy chain line arewithin set temperature ranges, and when a daisy chain line has a pipeheater that is over temperature range. More sophisticated remotemonitoring can be provided in another embodiment that includes asupervisory central monitoring station, which has a user interface and amonitor that can be used to display operational data of all of the pipeheaters controlled by the heater control system. In addition to visualdisplay of status indicators, audio alarms are included in some systemsto quickly alert operating personnel to “out-of-temperature-range”occurrences.

[0024] Other features and advantages of the invention will become clearfrom the following detailed description and drawings of particularembodiments of the heater control systems and associated combinationsand methods of operating the heater control systems steps of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate the preferred embodiments of thepresent invention, and together with the descriptions serve to explainthe principles of the invention.

[0026] In the Drawings:

[0027]FIG. 1 is an isometric view of the pipe heater control systemcomponents of this invention mounted on a typical pipe section,including an example of three local control modules mounted on pipeheaters in a daisy chain connection to a base unit;

[0028]FIG. 2 is a front elevation view of the example three localcontroller modules and base unit shown in FIG. 1;

[0029]FIG. 3 is an isometric view of the socket of this invention on apipe heater surface with a local controller module of this inventionpoised over the socket in position to be lowered onto and plugged ontothe socket;

[0030]FIG. 4 is an isometric view of the bottom of the local controllermodule;

[0031]FIG. 5 is an isometric view of the tops of the socket circuitboard and socket housing with the socket circuit board poised inposition to be assembled into the socket housing;

[0032]FIG. 6 is an isometric view of the bottoms of the socket housingand socket circuit board poised in position to be assembled together;

[0033]FIG. 7 is an enlarged cross-section view of a local controllermodule of this invention taken substantially along section line 7-7 ofFIG. 2;

[0034]FIG. 8 is a schematic diagram of the socket circuit board routingof power and signals between daisy chained inputs and outputs and to andfrom other pipe heater and local controller module components;

[0035]FIG. 9 is a functional block diagram of the pipe heater controlsystem of the present invention including a monitoring station incommunication with three pipeline heater systems having base units andlocal heater controller modules; and

[0036]FIG. 10 is a functional electrical block diagram of one of thebase units and local controller modules and interconnected pipe heatersof FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

[0037] A pipe heater control system 10 according to this invention isshown in FIGS. 1 and 2 with an example of three of the local controllerunits 100 of this invention mounted on three pipe heaters 97 in a daisychain connection to a base unit 92. The three pipe heaters 97 aremounted on a pipe P to be heated in a typical manner, for example, asdescribed in U.S. Pat. No. 5,714,738 issued to H. Hauschulz et al.,which describes the structures, materials, and uses of such pipe heatersand is incorporated herein by reference for all that it discloses. Whilesome of the pipe heater 97 structural details will be described below,suffice it to say at this point that each pipe heater 97 can be securedon the pipe P by one or more straps 21. The pipe heaters 97 and localcontroller modules 100 are connected together in daisy chain fashion bydaisy chain cords 98, which will be described in more detail below. Thefirst pipe heater 19 and local controller module 100 in the daisy chainare connected to the base unit 92 by an extension cord 94.

[0038] Essentially, as shown in FIG. 3, at typical pipe heater 97comprises a heating mat or core component 22 with an inside surface 23that is adapted to interface with the pipe P, a thermal insulation layer25 bonded to the outside surface 24 of the heating component 22 a jacketor partial jacket 26 from which the straps 21 extend. In the pipe heater97 shown in FIGS. 1-3, and as best seen in FIG. 3, a set of resistiveheater wires or heater elements 126 are embedded in the heating mat orcore component 22 and are powered by high-voltage alternating current(AC) electric power, typically 120 volts or 240 volts, 50 or 60 hertz,to produce heat, although other voltages and/or hertz power and otherkinds of heat producing components can be used.

[0039] In this invention, the local controller module 100 on each pipeheater 97 controls the high-voltage AC electric power to the resistiveheater wires 27 based on a set point temperature, as will be explainedin more detail below. Suffice it to say at this point that thehigh-voltage AC power is delivered to the pipe heaters 97 by theextension cord 94 from the base unit 92 and by the daisy chain cords 98.A temperature sensor 142, as best seen in FIG. 7, is embedded in thethermal insulation 25, preferably on the surface 24 of the heatingcomponent 22, so that it is not buffered from heat or temperature of theheating component 22 by any insulation 25 between it and the heatingcomponent 22. An electric circuit 101 in the local controller module 100compares a signal from the temperature sensor 142 with a set pointtemperature and, if the signal from the temperature sensor 142 indicatesthe temperature of the heating component 22 is less than the set pointtemperature or less than a certain range from the set point temperature,then the electric circuit 101 will turn “on” the high-voltage ACelectric power to the heater element 126 to produce more heat. On theother hand, if the signal from the temperature sensor 142 indicates thatthe temperature of the heating component 22 is higher than the set pointtemperature or higher than a certain range from the set pointtemperature, then the electric circuit 101 will turn “off” the highvoltage electric power to the heater element 126.

[0040] In the preferred embodiment, the electric circuit 101 in thelocal controller module 100 is powered by low voltage DC current, e.g.,9 volts, which is produced by a dc power supply in the base unit 92(FIGS. 1 and 2) and delivered to the local controller modules 100 by theextension cord 94 and daisy chain cords 98. The dc power supply producesthe low-voltage de power from the high-voltage AC power obtained by thebase unit 92 from public utility or other AC power source available inthe vicinity and delivered to the base unit 92 by a conventional powercord 91. It is preferred to place the dc power supply in the base unit92 rather than in individual local controller modules 100, even thoughthis arrangement requires more wires in the extension cord 94 and daisychain cords 98, for several reasons. First, dc power supplies thatproduce low-voltage dc current from high-voltage AC electric currentconsume substantial amounts of power that is manifested in creation ofsubstantial amounts of heat, which must be dissipated to avoid hightemperatures that could damage electric circuit components. Enough heatcan be dissipated naturally in ambient atmospheric or room temperatureenvironments, where the base unit 92 is usually situated, to avoid suchdamage to circuit components. Therefore, no bulky heat dissipationdevices are needed for such dc power supplies in the base unit 92. Onthe other hand, the local controller modules 100 are positioned on thepipe heaters 97, which are hot themselves. Therefore, it would be muchmore difficult to dissipate heat from a de power supply located in thelocal controller module 100 and would require at least bulky heat sinkmaterial with fins or other devices to dissipate heat produced by a dcpower supply. Second, providing a dc power supply at each localcontroller module 100, instead of at the base unit 92 only, wouldmultiply power consumed by the heater control system 10. Therefore, inthe interest of optimizing size, power consumption, and otherconsiderations, it is preferred to allocate the dc power-productionfunction for the local controller modules 100 to the base unit 92.

[0041] On the other hand, locating the heater control functions ofcomparing temperature sensor 142 signals with set point temperatures andswitching the high-voltage AC power “on” and “off” at the localcontroller modules 100 is preferable over providing those functions inthe base unit 92 or elsewhere. For example, this allocation of functionsallows independent temperature control of each pipe heater 97 withminimal circuitry 101 without the need for dedicated AC power and datacommunication wires from the base unit to each individual pipe heater97, which would inhibit the simple daisy chain connectability of thelocal controller modules 100 to the base unit 92 according to thisinvention.

[0042] It is feasible with this configuration, though, to includeseveral, preferably two, data communications wires in the extension cord94 and daisy chain cords 98 for some useful data that can be bussedbetween the local controller modules 100 and the base station 92, suchas data that would indicate whether all of the daisy chained heaters 97are operating within their respective set point temperature ranges or atleast one of them is outside (above or below) its set point temperaturerange so that such information can be displayed at the base unit 92. Itis also feasible to bus individual set point temperature instructions torespective local controller modules 100 in the daisy chain via the twocommunications links in the extension cord 94 and daisy chain cords 98,as will be discussed in more detail below. Specific data for aparticular local controller module 100 can be encoded with anidentification that is accepted only by that particular local controllermodule 100. Such encoded addressing to electronic devices is known andunderstood by persons skilled in the art.

[0043] A significant feature of this invention is the combinationmodular and daisy chained connectivity of the pipe heaters 97 and localcontroller modules 100 to the base unit 92 via socket 200 in the pipeheaters 97, as best seen in FIGS. 1-7. Referring first primarily to FIG.3, the socket 200 has a socket frame 202 that is either molded as anintegral part of the jacket 26 or bonded to the jacket 26 and a socketcircuit board 204 that is mounted in the socket frame 202. The socketcircuit board 200 enables the combination modular and daisy chainedconnectivity of this invention by serving a number of functions,including: (i) routing the high-voltage AC electric power from one daisychain connector 206 to the other daisy chain connector 208, both ofwhich are integral parts of the socket circuit board 200; (ii) routinghigh-voltage AC power to the local controller module 100 for switching“on” and “off”; (iii) routing switched “on” high-voltage AC power fromthe local controller module 100 to the heater element 126; (iv) routinglow-voltage de power from one daisy chain connector 206 to the otherdaisy chain connector 208; (v) routing low-voltage de power to thecircuit 101 (FIG. 7) to the local controller module 100; (vi) routingtemperature sensor signals from the temperature sensor 142 (FIG. 7) tothe local controller module 100; (vii) routing data communication linksfrom one daisy chain connector 206 to the other daisy chain connector208; (viii) routing data communication links to the local controllermodule 100; (ix) providing high-voltage AC connector 210 and low voltagedc connector 212 for “plug-in” type mounting of the local controllermodule 100 to the pipe heater 97; and (x) providing daisy chainconnectors 206, 208 for “plug-in” connection of the daisy chain cords 98or the extension cord 94 to the pipe heater 97.

[0044] The bottom of the local controller module 100 is shown in FIG. 4,when viewed in combination with the top of the socket circuit board 204,illustrates the male parts 210′, 212′ of connectors 210, 212,respectively, which plug into the corresponding female parts of thoseconnectors 210, 212 to facilitate the “plug-in” mounting or docking ofthe local controller module 100 on the socket 200 of pipe heater 97. Allof high-voltage AC, low-voltage de, temperature sensor signals, and datalinks to and from the local controller module 100 are established bymerely docking or plugging the local controller module 100 into thesocket 200. Then, when the daisy chain cords 98 are plugged into thesockets 206, 208 through the openings 297, 209 in the housing 214 of thelocal controller modular 100, the retainer bars 216, 218 interact withthe plug ends 99 of daisy chain cords 98 to help retain the localcontroller module 100 on the socket 200. The local controller module 100can be removed from the pipe heater 97 by unplugging daisy chain cords98 from connectors 206, 208 and unplugging the local control module 100from sockets 210, 212 by simply pulling the local controller module 100away from the socket 200.

[0045] The mounting of the socket circuit board 204 in the socket frame202 is illustrated in FIG. 6, where the socket circuit board 204 ispoised for insertion into the bottom of the socket frame 202. Apertures222, 224, 226 in the top of socket frame 202 accommodate insertion ofconnecters 206, 208, 210, 212 through the socket frame 202. The socketframe 202 is preferably slightly elastic, so it can be deformed enoughto insert the edges of the socket circuit board 204 over the ledges 232,234 to retain the socket circuit board 202 in the socket frame 202.Either prior to or after such insertion, the high-voltage AC wire leads236, 238 to the heater element 126 and the wire leads 242, 244 from thetemperature sensor 142 are soldered to appropriate posts 246, 248 and252, 254, as best seen in FIG. 7. A plurality of other posts 240 andtraces 250 illustrated diagrammatically in FIG. 6 provide the routingfunctions of the socket circuit board 204, as explained above. There isenough room in cavity 230 into which the wire leads 236, 238, 242, 244can be folded as the jacket 26 and socket 200 are lowered and bondedonto the exterior surface 22 of the thermal insulation 25 of the pipeheater 97 to position the socket 200 over the cavity 230.

[0046] In the local controller module 100, the control circuit 101,which will be provided in more detail below, is positioned primarily ona controller circuit board 256. The controller circuit board 256 ismounted in the housing 214, and the top and bottom parts of the housing214 with the circuit board 256 are held together by a pair of screws258, 259.

[0047] As illustrated schematically in FIG. 8, the preferred embodimentheater control system 10 of this invention has six wire conductors inthe extension cord 94 and in each daisy chain cord 98, and all six ofthem trace straight through the socket circuit board 204 from connector206 to connector 208 to accommodate the daisy chain connection of oneset of pipe heater 97 and local controller module 100 to another. Twowires 124, L1 and L2, carry the high-voltage AC current for powering theheater elements 126. One of the traces L1, L2 is tapped to the heaterelement 126 and the other passes via connector 212 to some type of powerswitch 130 in the local controller module 100, as will be described inmore detail below, before returning back through connector 212 andsocket circuit board 204 to the heater element 126. The low voltage(e.g., +9 volts) dc power is carried on two wires 120 (+9 volt andcommon), both of which are also traced straight through the socketcircuit board 204 from connector 206 to connector 208. Both the +9 voltand common (COM) traces are tapped into the local controller module 100via connector 210 to power the local controller process circuit 101.Finally, two data wires 122, A and B, are also traced straight throughthe socket circuit board 204 from connector 206 to connector 208, andboth are tapped through connector 210 for passing data into and out ofthe local controller process circuit 101, as will be explained in moredetail below. Thus, it is clear from FIG. 8 that each pipe heater 97 andlocal controller module 100 operate off all of the wires 124, 120, 122(L1, L2, +9V, COM, A, and B) in electrical parallel connection to otherpipe heaters and local controller modules 100 in a daisy chain accordingto this invention. The two wires 143 are purely local and not includedin the extension cord 94 or daisy chain cords 98, but they trace throughthe socket circuit board 204 from the temperature sensor 142 tot helocal controller process circuit 101 via the connector 210 for thepurposes described above.

[0048] The preferred heater control system 10 is illustrateddiagrammatically in FIG. 8 and generally includes an optional centralmonitoring station 72 with a user interface 74 (i.e., a monitor, with orwithout a touch screen capability, a keyboard(s), a mouse, and otherperipheral computer interface equipment), a central processing unit(CPU) 76 in communication with the user interface 74 and memory 78 whichmay contain software for use in monitoring and controlling heaters andheater controllers, databases with temperature “recipes” for variousprocesses and other temperature and maintenance information, and acommunication port 80 for receiving and transmitting digital data. Thecentral monitoring station 72 is connected with communication lines 81,82, and 83 to, for example, three pipe heater control systems 84, 86,and 88, on pipes 85, 87, and 89, respectively. During operation, thecentral monitoring station 72 allows a user at a remote location toquickly monitor the temperature of each heater in the heater controlsystems 84, 86, and 88 and in some embodiments, to transmit commands viathe communication lines 81, 82, and 83 to change the temperaturesettings of the individual heaters or otherwise control operation (e.g.,turn the heaters on and off). In this fashion, a single centralmonitoring station 72 can be used to control and monitor a very largenumber of heaters and heater systems (although only three are shown forease of illustration). To more fully understand the operation and use ofthe central monitoring station 72, its integration with a single pipeheater control system 86 will be discussed in detail in connection withthe description of the components of the control system 86. Of course,it will be understood from the following discussion that the controlsystem 86 may be utilized separate from the heater control system 10.

[0049] It is preferred that the pipe heater control system 86 providecontrol and supply power to a number of controllers and heaters with theuse of a minimum number of leads, wires, and/or lines to avoid the rat'snest problem that is prevalent with prior art control systems. In thisregard with reference to FIGS. 9 and 10, the pipe heater control system86 includes the base unit 92 that communicates with the centralmonitoring station 72 via communication line 82 and receives AC powerfrom a single AC power supply 90 over line 91. The base unit 92 includesa digital input and output device 116 for communication with the centralmonitoring station 72 and a digital I/O 112 for transmitting commandsand information requests from the central monitoring station 72 and thebase station 92 to satellite controllers 96, 100, 104 and for receivingdigital signals from the same controllers 96, 100, 104. In a preferredembodiment, both of these communication interfaces are configured to useboth the EIA RS-232 and RS-485 standards at a fixed baud rate of 9600baud. The base unit 92 includes an optional ground fault interrupt 106and a 12-amp circuit breaker 108 for increasing the operating safety ofthe control system 86 and for isolating the local controller modules 100from the AC power supply 90 in the event of a short circuit or groundfault condition. Additionally, the base station 92 includes a DC powersupply 110 (e.g., a 9-volt DC power supply) for supplying DC power forelectronic temperature control components of each local controllermodule 100.

[0050] In the preferred embodiment base unit 12 illustratedschematically in FIG. 10, the AC power output, DC power output, anddigital I/O lines are integrated and/or contained within a singlecommunication/power extension cord 94 that is passed to the first localcontrol module 100. Further, the communication/power extension cord 94is illustrated as coiled in FIG. 9 because this further enhances ease ofinstallation and maintenance as the specific location of each localcontroller module 100, and the distance between the same may vary witheach application. With the combination of a coiled cord 94 (as well asdaisy chain cords 98) and integration of power and communication linesinto a single cord 94 (and daisy chain cords 98), the control system 86is able to readily achieve the goals of minimizing the complexity of thesystem, reducing space requirements, and increasing the ease ofinstallation and replacement (i.e., each line 94, 98 and localcontroller module 100 can be individually plugged into the system 86).

[0051] To allow a single line to be fed from the base unit 92, it isimportant that power and communication lines be passed through eachlocal controller module 100 to allow the local controller modules 100 tobe daisy chained together. This integration of power and temperaturesensing and control at each local controller module 100 is achieved asillustrated in the functional block diagram of FIG. 10.

[0052] Significantly, this integration of control functions allows eachof the local controller modules 100 to be housed in a single housing 148as illustrated in FIGS. 1-7. Additionally, the size of the housing 148is maintained relatively small (i.e., a width, W, of less than about 64mm, a height, H, of less that about 32 mm, and a length, L, of less thanabout 70 mm). The local controller module 100 and housing 148 areconfigured, in this exemplary embodiment, for mating with a docking portor socket 200 attached to a wrap around flexible pipe heater 97 asdescribed above.

[0053] Referring again to FIG. 10, the local controller module 100 isconfigured to receive AC power from the base unit 92 via cord 94 onleads 124 which are directed into the heater 97. It should be noted thatFIG. 10 is schematic, so the exact locations of lines e.g., line 120,122, 124 etc. are not shown in FIG. 10. See FIG. 8 and relateddescription for the preferred location of those lines or wires 120, 122,124 in the socket circuit board 204, as explained above. The heater 97includes heater element 126 that operates on the AC power on leads 124and is electronically controlled (i.e., turned on and off) via leads 128and 131 by opto-coupler zero voltage power switch 130 (although otherelectronic switching devices may readily be utilized). The localcontroller module 100 brings DC power in with leads 120 which power themicroprocessor 134 and other electronic components via leads 132. Themicroprocessor 134 is included in the local controller module 100 toprovide better control over the temperature settings of the heater 97,to operate operational displays 146 at the controller 100, to operatethe power switch 130 to maintain temperatures within a desired and useradjustable range, and to provide digital communication capability withthe base station 92 and in some cases, the monitoring station 72.

[0054] During operation, the temperature sensor 142 (e.g., a thermistor,thermocouple, or the like) which is positioned adjacent the heatersurface 127 responds to temperature changes in the heater surface 127and outputs on lead 143 a representative signal (such as a voltagesignal). Sense amplifier 144 amplifies this signal and transmits ananalog signal to the microprocessor 134 which includes an analog todigital converter 136. The microprocessor 134 is configured to processthe digital signal from sense amplifier 144 to determine the temperatureof the heater surface 24. The microprocessor 134 then determines if theheater surface 24 temperature is within an acceptable range about atemperature set point.

[0055] According to the invention, the controller 100 is preferablyadapted to allow a user to control (i.e., set and later adjust) thetemperature at which the heater 97 is operated. Typically, this isachieved by setting a temperature set point and, in some embodiments, arange of variation about this set point (or the temperature band aboutthe temperature set point may be fixed by the electronic temperaturecontrol technique utilized, e.g., if on-off control is used with turningon a heater at a low temperature setting and turning the heater off at ahigh temperature setting). As illustrated in FIG. 4, the controller 100includes an 8-position dip switch 140 which allows the user to eithermanually set the temperature set point (e.g., by setting the binarynumber of a desired temperature in the 8 position dip switch 140) orremotely by setting all the switches of the dip switch 140 to zero orother designated remote mode settings and then remotely communicating atemperature set point to the microprocessor 134 via digitalcommunication lines 122 from the monitoring station 72 (which is storedin memory of the microprocessor 134). As illustrated, the dip switch 140is accessed by unplugging the local controller module 100 from thedocking port or socket 200 of the heater 97.

[0056] During operations, the microprocessor 134 compares thetemperature determined from signals from the temperature sensor 142 withthe temperature setting of the 8 position dip switch 140 via lines 141or the temperature received from the monitoring station 72 to verifywhether the heater surface 127 is within an acceptable temperature range(such as, for example, within 5° C and more preferably within about 2°C. of the temperature set point). If the heater surface 127 temperatureis under the acceptable temperature range, the microprocessor 134functions to operate the switch 130 to operate the heater 97 and tocommunicate this low temperature to the base station 92 over leads 138and 122.

[0057] Referring to FIG. 10, the base unit 92 may have its own operationstatus display 114 and/or an alarm status relay 118 for activating audioand visual alarms either at the base station 92 or at a remote location(e.g., a flashing light that is readily visible from a distance). In apreferred embodiment, the operation status display 114 “lights” a blueLED when at least one of the pipe heaters 97 is under its settemperature range, lights a green LED when all of the pipe heaters 97are within their set temperature ranges, and lights a red LED when oneof the pipe heaters 97 is above its set temperature range. The base unit92 concurrently transmits the temperature and operating information foreach pipe heater 97 to the monitoring station 72 where it can bedisplayed on the user interface 74 and/or stored in memory 78.

[0058] Referring again to FIG. 10, the microprocessor 134 also functionsto operate a local display 146 with three colored LEDs similar to thatdiscussed for the base unit 92 that enables a user to quickly, visuallymonitor each of the pipe heaters 97 in a pipe line. The LED display 146is readily visible on the upper, exterior portion of the controllerhousing 148 (see FIG. 3). The microprocessor 134 continues to monitorand compare the heater surface 127 temperature, and, once thetemperature reaches a predetermined point within the temperature range,the microprocessor 134 functions to operate the switch 130 to turn offthe heater 97, communicate “within range” information to the base unit92 (and thereby, the monitoring station), and operate the display 146 ofthe local controller module 100. The microprocessor 134 then continuesto monitor the temperature of the heater surface 24 to communicate ifthe temperature is over or out of an acceptable range and to repeat theabove operations when the temperature falls under the preset temperaturerange. The control logic exercised by the microprocessor 134 can be asimple on/off control, a version of PID control, and other controlfunctions.

[0059] In the above manner, the temperature of each pipe heater 97 canbe set and maintained within a relatively tight temperature range (suchas a 1 to 2° C. range). Significantly, the use of a monitoring station72 and remotely programmable local controller modules 100 allows a userto establish and rapidly change the temperatures of each of the pipeheaters 97 to establish relatively complex recipes for changingprocesses. Further, the configuration of the heater control system 10allows a user to remotely and locally monitor the operation of eachlocal controller module 100 and pipe heater 97 to enhance processmonitoring and to decrease the time spent on troubleshooting. To furthermaintenance, each of the local controller modules 100 is designed toallow a user to unplug a single controller 100 and/or its associatedpower/communication cords 94, 98 and plug in replacements.

[0060] During operation, the base unit 92 operates to at leastperiodically, such as once every 2 seconds or some other fixed timeperiod, poll the connected local controller modules 100 for status(e.g., temperature) and diagnostic information. To monitor the life ofcertain components of the local controller module 100, a countermechanism or routine may be included within the microprocessor 134 totrack the times they are operated. For example, electromechanical relaystypically have a fixed operating life and it may be useful to include acounter for each included electromechanical relay to count the timesthey are activated. Once the preset number is reached, themicroprocessor 134 sends this information to the base unit 92 toestablish a maintenance flag for the local controller module 100.

[0061] Since numerous modifications and combinations of the above methodand embodiments will readily occur to those skilled in the art, it isnot desired to limit the invention to the exact construction andprocesses shown and described above. For example, in FIG. 9, a separateAC power supply and base station was shown for each pipe line and thisconfiguration was selected to easily comply with certain electricalsafety standards. Of course, the illustrated heater control system 10can be modified to include a single AC power source and a single basestation that together provide AC power to multiple control systems 84,86, and 88. Also, in lieu of separate data communications lines or wires122, data could be sent in other ways know to persons skilled in datatransfer arts, for example, infrared transmitters or receivers, fiberoptics, or radio frequency (RF) communications over the AC power lines124, and the like. Accordingly, resort may be made to all suitablemodifications and equivalents that fall within the scope of theinvention as defined by the claims which follow. The words “comprise,”“comprises,” “comprising,” “include(s),” and “including” when used inthis specification and in the following claims are intended to specifythe presence of stated features or steps, but they do not preclude thepresence or addition of one or more other features, steps, or groupsthereof.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A heater controller formonitoring and controlling the operation of a heater, comprising: an ACpower inlet for connecting the heater controller to an AC power sourceto receive AC power; an electronic temperature controller having atemperature sensor adjacent a heater surface of the heater for sensingthe temperature of the heater surface and in response transmitting asignal and an electronic switch connected to the heater element and thetemperature sensor, wherein the electronic switch operates to receiveand process the signal from the temperature sensor and to selectivelyapply the received AC power to the heater element in response to thesignal to control the temperature of the heater surface within atemperature range about a temperature set point; and a power supplyconnected to the AC power inlet and the electronic temperaturecontroller adapted for supplying the received AC power to the electronictemperature controller in an acceptable power form for use in operatingthe temperature sensor and the electronic switch of the electronictemperature controller.
 2. The heater controller of claim 1, furtherincluding an AC power outlet connected to the electronic switch and theAC power inlet adapted for outputting AC power to a second heatercontroller connected to the AC power outlet.
 3. The heater controller ofclaim 1, wherein the acceptable power form for the electronictemperature controller is DC power and the power supply includes an ACto DC converting device.
 4. The heater controller of claim 1, whereinthe electronic switch includes a temperature input for setting thetemperature set point.
 5. The heater controller of claim 4, wherein thetemperature input is an 8-position dip switch.
 6. The heater controllerof claim 1, wherein the temperature range is less than about 5° C. oneither side of the temperature set point.
 7. The heater controller ofclaim 1, further including a housing configured to contain the AC powerinlet, the power supply, and the electronic temperature controller andfurther including an operational status display connected to thetemperature sensor adapted for providing a heater surface temperatureindication based on the signal from the temperature sensor on anexternal surface of the housing.
 8. The heater controller of claim 7,wherein the operational status display includes a first LEDcorresponding to a heater surface temperature under the temperaturerange, a second LED corresponding to a heater surface temperature withinthe temperature range, and a third LED corresponding to a heater surfacetemperature over the temperature range.
 9. The heater controller ofclaim 7, further including wherein the housing has a width of less thanabout 64 millimeters, a height of less that about 32 millimeters, and alength of less than about 70 millimeters.
 10. The heater controller ofclaim 1, further including a transmitter connected to the temperaturesensor for transmitting temperature information based on the signal to aremote monitoring location.
 11. The heater controller of claim 1,wherein the switch comprises a zero voltage switch.
 12. A heater controlsystem for monitoring and controlling operation of a plurality ofheaters, comprising: a heater controller attached to each of theheaters, wherein each heater controller includes an electronictemperature sensing and control system for sensing the temperature of aheater surface of the attached heater and for controlling operation ofthe heater based on the sensed temperature and further includes a DCpower inlet and outlet, a communication inlet and outlet, and an ACpower inlet and outlet; and a base station connected to a first of theheater controllers, the base station being configured for communicatingwith each of the heater controllers and providing AC and DC power toeach of the heater controllers through the first heater controller. 13.The heater control system of claim 12, wherein the heater controllersare communicatively and electrically connected to adjacent heatercontrollers through the DC power inlets and outlets, the communicationinlets and outlets, and the AC power inlets and outlets of the heatercontrollers.
 14. The heater control system of claim 13, wherein theelectronic temperature sensing and control system is connected to the DCpower inlet and the communication inlet and the heater is connected tothe AC power inlet.
 15. The heater control system of claim 13, whereinthe communication connection and the electrical connection betweenadjacent heater controllers comprises a single cable having a coiledconfiguration, whereby distances measured between the adjacent heatercontrollers can vary within a predetermined range.
 16. The heatercontrol system of claim 12, wherein the electronic temperature sensingand control system includes a temperature sensor for sensing thetemperature of the heater surface and in response transmitting a signal,an electric switch in contact with a heater element of the heater andthe AC power outlet, and a processor for processing the signal andoperating the electronic switch based on the processed signal to operatethe heater element.
 17. The heater control system of claim 16, whereinthe electronic temperature sensing and control system further includes atemperature input communicatively linked to the processor for setting atemperature set point, the processor being configured to compare theprocessed signal with the temperature set point to operate theelectronic switch to maintain the heater surface in a temperature rangeabout the temperature set point.
 18. The heater control system of claim17, wherein the temperature input is an 8-position dip switch.
 19. Theheater control system of claim 17, wherein the temperature range is lessthan about 5° C.
 20. The heater control system of claim 17, wherein theelectronic temperature sensing and control system includes an operationstatus display connected to the processor for visually displaying at theheater controller a first state corresponding to a sensed temperatureunder the temperature range, a second state corresponding to a sensedtemperature within the temperature range, and a third statecorresponding to a sensed temperature above the temperature range. 21.The heater control system of claim 17, wherein the base station includesan input and output device for communicating operating information toand from the heater controllers, the operating information includingsensed temperatures and temperature set point commands whereby the basestation is operable to remotely set the temperature set point of each ofthe heaters.
 22. The heater control system of claim 21, furtherincluding a second base station connected to a heater controller, notlinked to the first heater controller, and a monitoring stationcommunicatively linked to the base stations, the monitoring stationbeing configured for receiving and transmitting the operatinginformation to and from each of the base stations.
 23. The heatercontrol system of claim 12, wherein the base station includes an ACpower inlet for receiving AC power from an AC power source and includesa DC power supply for converting the received AC power to DC power andfor transmitting the DC power to the heater controllers.
 24. A method ofcontrolling operation of a series of heaters, comprising: coupling aheater controller to each of the heaters, each heater controller beingpositioned with a temperature sensor of the heater controller adjacent aheater surface of the coupled heater and including an AC power inlet andoutlet and an electronic switch electrically connected to thetemperature sensor and electrically contacting the heater surface duringthe coupling; connecting an AC power source to the AC power inlet of afirst of the heater controllers; providing AC power to each of the otherheater controllers via the AC power outlet of the first heatercontroller by electrically connecting adjacent ones of the heatercontrollers at the AC power inlets and outlets, respectively, of theadjacent heater controllers; setting a temperature set point for each ofthe heater controllers; sensing a temperature of each of the heatersurfaces of the heaters with the temperature sensors; and operating theelectronic switch of each of the heater controllers in response to thesensed heater surface temperature to maintain each of the sensed heatersurface temperatures within a temperature range about the temperatureset point of the corresponding heater controller.
 25. The method ofclaim 24, wherein the temperature setting is completed manually at eachheater controller by operating a temperature input.
 26. The method ofclaim 24, wherein the temperature setting is completed remotely bytransmitting operating information to each heater controller from a basestation, the heater controllers being communicatively linked with thebase station.
 27. The method of claim 24, further including convertingwithin each heater controller the received AC power to DC power andsupplying the DC power to the temperature sensor and the electronicswitch.
 28. The method of claim 24, further including displaying at eachheater controller an operational state of the heater coupled to theheater controller.
 29. The method of claim 28, wherein the operationalstates are selected from the group consisting of under the temperaturerange, within the temperature range, and over the temperature range. 30.The method of claim 29, wherein the temperature range is less than about5° C.